Letoff mechanism for looms



1952 J. PICANOL 2,585,167

LETOFF MECHANISM FOR LOOMS Filed Sept. 50, 194': 2 SHEETS-SHEET 1ATTORNEYS Feb. 12, 1952 J. PICANOL 2,585,167

LEZTOFF MECHANISM FOR LOOMS Filed Sept. 50, 1947 2 SI-IEETS-SHEET 2crime Pica/1o //YVf/770/? Arrow/15y:

Patented Feb. 12, 1952 STATES PATENT OFFICE Application September 30,1947, Serial N 0. 777,057 In Belgium December '3, 1940 :3 Claims. (01.139--110 -Ihe present invention relates to a warp let-off mechanism forlooms of the kind in which the warp leaving the beam is passed over awhip-roll mounted on a movable carrier, which carrier balanced by aspring or acounterweight, controls through suitable means the let-offmotion of the beam, according-to the tension changes of the warp.

It isessential for good weaving to maintain a constant tension in thewarp-yarns.-

Warp tension changes have so many difierent causes that it ispractically impossible to foresee them and to build-individualcorrecting devices for each of them.

An object of this invention is to provide a warp let-off mechanism ofthe above mentioned kind, through which a constant tension is maintainedin the warp-yarns, irrespective of the diameter of the warp beam and ofall other working conditions of the loom.

Another object of this invention is to provide means for adjusting thewhip-roll position in height without causing any alteration in thebalancing spring action.

The device, constituting the object of the invention, only uses thetension changes of the warp threads for operating the control mechanismof the unwinding of the warp from the warp-beam.

With the foregoing objects in view, in awarp let-ofimechanism of thekind referred to, made according to the present invention, there is providedat each loom side a spring balanced-whiproll carrier, over whichWhip roll the warp passes. These carriers'are rotatably mounted on anaxle which is disposed on therlocus of all points for which theresultant of the variable forces acting on the whip-roll during theunwinding of the beam. provides a torque of constant value, oneofsaidlevers in combination with. bell-crank levers and connecting rods,adjusts the amount ctr-motion ransmitte th ou h t e a word t heepe et np w 0f the ratchet wheel. which centreshe retatien e th arp amorder o emit ad ustm t. in hei htens the w ip o lwit eut cau n any a r io s in. te ba nci spr n aetion. he emmen xle of: th w 91 c er has e n se r d o espsi-ii ta r xed t ea eem. i e. the balancing spring bearing with oneend. on the whip-roll carrier and its other end being; connected bymeans of arod to said adjustable suppert.

Qtherteatures accompanying the invention willbecome appa ent iro sv the.renewing description 2 and drawings. In the accompanying drawings anillustrative embodiment of my inventionis shown, in which:

Fig. l is a schematic view of the princi'pa kinematic elements of themechanism according to the invention. 1

Fig. 2 is an explanatorydiagram.

Figure 3 is a diagram illustrating the manner of determining graphicallythe locus of the-rotationcentre of the whip-roll carrier.

Figure 4 is a perspective schematic view illus trating a constructionalembodiment of a -device according to the invention. 7

Figures 5 and 6 show a graphical manner of determining the'resultingforce acting on the whip-roll. 5 V 4 Referring to the drawings, theyarns 1, unwound from beam 2 bear on-a whip-roll 3. This roll 3 bears ateach loomside on one of the ends of a carrier 4, the other end of whichis connected to a balancing spring 5. The yarns l exert on roll 3 apressure proportional to their tension.

To any tension change corresponds an oscillation of the carrier 4. Thesemovements are transmitted to a lever 6 by means of connecting rod 8, abell-crank lever 1 and a second connecting rod 9'.

The stroke of the bell-crank'lever 1- has been limited bystops i0 and H,the lever '6 is at one end connected by means of a pivot -l 3 toth'epawlcarrier l4.

The pawl-carrier l4 bears one or more pawls l5 and operates a ratchetwheel l6, which through bevel gears I! and I8 and a worm-drive I 9;rotates the warp beam 2. I v v The other end of the lever B bears aroller 21'! which projects into the arcuate slot 2| of a link lever 22pivoted to a fixed pivot 23. This link lever 22 being connected to thelay sword I2'by means of a rod 24.

The arcuate slot of the link-lever 22 enables the axis of the roller 20to coincide with the oscillation axis 23, in sucha way that 'when'thishappens, the motion of lever 6 is insignificant.

The arcuate slot 2| also allows lever B to move freely around itspivoting point [3, under the action of the whip-roll carrier 4; throughthe kinematic system 8, 1, 9.

Hence to each angular displacement of the whip-roll carrier 4;corresponds an angular displacement of the lever 6 around its pivot 23.

Any angular displacement of the lever 6 causes a corresponding change ofthe stroke of its horizontal motion. Indeed the distance between theaxis of the roller 20 and theoscillating center-23 change in tension ofthe warp yarns influences the whip-roll carrier which will consequentlychange the amplitude of the rotation motion of the warp beam.

Great care must be given to the selection of the position of therotation axis 25 of the whip-,

roll carrier 4. Consideration has in cfact to be given to the variationsof diameter of the beam,

whether on starting on a new beam or during the course of operation. Asthe whip-roll carrier 7 4 is balanced by an elastic device, in this casea coiled spring 5, it is necessary to arrange the components so that thespring action is substantially constant under all working conditions.

Now, as is indicated in the diagrams of Figures 2, 5 and 6 with a beamof diameter D, the layer of yarns will be in the position -I' while witha beam of diameter d, the layer of yarns will be in the position I".

According to the positions I and I" of the layer of yarns, there areexerted on roller 3 pressures which are variable in direction and size,the resultants of which are denoted respectively R and R, these tworesultants being different both in direction and in size. In the diagramof Figures 2, 5 and 6, consideration has been given to the additionalforce produced by a second roller 26, which is necessary in order that,co-operating with roller 21 and the eccentric 2B, consideration may begiven to the length of the yarn in the course of the alternation of theshed. On whip-roll 3 is thus introduced a resultant R of the pressuresexerted on roll 25. Resultants R and R" force into considerationresultant R' if use is made of such a roll 26. Hence, it is necessarythat the rotation centre 25 of the whip-roll carrier. 4 be located insuch a way that the torque originated by the pressure of yarns I, ispractically constant, whatever be the diameter of the beam. The diagramof Figure 3 shows how a geometrical locus has been established of allthe points around which resultants R, R, provide a constant torque. Onthis geometrical locus will be selected the point most suitable to themechanical layout of the loom. Thus, once this rotation centre 25 isestablished, the spring 5 will work in conditions nearly identical,whatever be the diameter of the beam, which means whatever be theinclination of the layer of yarns on roll 3.

The above are the essential elements of the automatic let-off.Complementary or accessory devices may of course be added, in order toensure accuracy of operation of the kinematic system. More particularlyit will be necessary to provide means for varying the initial tension ofthe compensatory spring 5 for altering the initial position of therotation axis 25 of the whip-roll carrier 4, and the like.

An embodiment is shown diagrammatically in perspective view in Figure 4.In this device, the layer of yarns l unwound from beam 2, presses asshown on the whip-roll 3; the spindle of the latter bears on the end ofa carrier 4 secured on a spindle 25. The other end of this carrier 4 isprovided with a series of grooves 29 engaged by two fingers 30 fixed ina niembei 3|, to which is connected the compensating spring 5. The otherend of this spring is secured to a fixed point. Hence by varying theposition of the member 3|, the position and consequently the tension ofspring 5 is varied. The spindle 25 around which the carrier 4 oscillatesis mounted on a support 32, which is rotatable around a fixed spindle33. Slots 34 in the support 32 are engaged by fixing bolts 35, whichhold the support 32 firmly in the desired position relatively to theframe. By these means it is possible to modify the initial position ofthe spindle 25, and, consequently of the whiproll 3. The inclination ofthe warp can thus be modified. The fixed point 36 to which is attachedthe compensating spring 5, is connected to the support 32 by a rod 31.By means of this arrangement the characteristics of the compensatingspring in relation to the whiproll carrier 4, are constant, whatever be;the position of the spindle 25.

A secondary roll 26 is supportedby a lever 38, ending in a roller 21.The latter is in permanent contact with an eccentric 28 mounted on thecrankshaft of the loom or connected in an appropriate manner to saidcrankshaft. This arrangement provides for stretching the yarn in such amanner that the tension remains. practically constant, whatever be theposition oithe shed. It will be understood that the necessary length ofyarns is greater for the extreme positions, i. e., for the more inclinedpositions, than for the median position, viz, when the. yarns form anextension of the woven material. For this purpose, roll 26 stretches theyarn when the latter is approaching the intermediate position, in such amanner that a constant. draft is maintained.

The whip-roll carrier 4 is connected to lever B by a connecting rod 8, abellcrank lever I and a second connecting rod 9. The latter is connectedat its other end to an intermediate point of lever 6, which can rotatearound theend l3, its, other end being provided with a roller 20 in themanner described above. Lever 6 is connected with the pawl-carrier I4.In this case three pawls are provided (only one of whichis shown in thedrawings) which respectively engage the ratchet wheel, one over thewhole length of a ratchet tooth, another over the two-thirds and thethird over a third of the length of the same tooth. In this manner theratchet-wheel [6 can be displaced through a minimum angle correspondingto one third of a tooth lengthor any multiple of a third of a toothlength. This minimum angle could of course be diminished by increasingthe number of pawls and the number of teeth of the ratchet wheel. Theratchet wheel It; drives the beam 2 through any suitable mechanicalmeans. Y

By means of the device above described, the means explained previouslycan thus be applied with precision, to provide a practically constanttension on all the yarns, whatever be the causes which tend to vary thistension, making provision for the different numerous requirements of theweaving industry and to the difierent characteristics of the yarns, orof 'the woven material.

I claim:' e 1. In a loom having a lay sword, and a, lever transmittingmotion, a positive warp let-oil mechanism having a whip-roll, awarp-beam with a pawland ratchet wheel-mechanism, a

whip-roll carrier at each loom side, spring means for balancing saidwhip-roll carriers, an axle rotatably supporting said whip-rollcarriers, said axle being located at the geometrical locus of all thepoints for which the resultant of the variable forces acting on thewhip-roll during the unwinding of the warp-beam provides a practicallyconstant torque, a bell crank lever having a fixed pivot pin, aconnecting rod transmitting the oscillations of one whip-roller carrierto said bell crank lever, and a second connecting rod pivoted to an endof said bell crank lever, and controlling the adjustable stroke of thelever transmitting motion from the lay sword to the operating pawl ofthe warp-beam ratchet wheel.

2. In a loom having a lay sword, a positive warp let-off mechanismhaving a whip-roll, a warp-beam with a pawl and ratchet wheel mechanism,a whip-roll carrier at each loom side, spring means for balancing eachof said whiproll carriers, an axle rotatably supporting said whip-rollcarriers, said axle being located at the geometrical locus of all thepoints for which the resultant of the variable forces acting on thewhip-roll during the unwinding of the war beam provides a practicallyconstant torque, a bell crank lever having a fixed pivot pin, aconnecting rod which transmits the oscillations of one whip-rollercarrier to said bell crank lever, a second connecting rod which ispivoted to an end of said bell crank lever, a link lever pivoted to afixed pivot and having an arcuate slot formed therein, a lever pivotedat one end to the lay sword and at its other end to said link lever, anintermediate lever pivoted to the pawl carrier, and a roller projectinginto said arcuate slot and fixed to an end of said intermediate lever,the position of said roller in said arcuate slot being controlledthrough said second connecting rod under the action of the warp-tension.

3. In a loom having a lay sword and a frame, a positive warp let-offmechanism having a whiproll, a warp-beam with a pawl and ratchet wheelmechanism, a whip-roll carrier at each loom side, spring means forbalancing each of said whip-roll carriers, an axle rotatably supportingsaid whip-roll carriers, said axle being located at the geometricallocus of all the points for which the resultant of the variable forcesacting on the whip-roll during the unwinding of the warpbeam provides apractically constant torque, a bell crank lever having a fixed pivotpin, a connecting rod which transmits the oscillations of onewhip-roller carrier to said bell crank lever, a second connecting rodwhich is pivoted to one end of said bell crank lever, a link leverpivoted to a fixed pivot and having an arcuate slot formed therein, alever pivoted at one end to the lay sword and at its other end to saidlink lever, an intermediate lever pivoted to the pawl carrier, a rollerprojecting into said arcuate slot and fixed to an end of saidintermediate lever, the position of said roller as to said arcuate slotbeing controlled through said second connecting rod under the action ofthe warp tension, a sup port adjustably fixed to the loom frame, saidaxle of the whip-roll carriers being secured to said support, saidspring means comprising a balanc ing spring having a fulcrum pin, and arod connected with said fulcrum pin and linked to said support, wherebythe adjustment in height of the whip-roll position, and consequently ofthe warp yarns, causes no alteration in the balancin spring action.

JAIME PICANOL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 660,834 Bennett Oct. 30, 19001,463,966 Northrop Aug. 7, 1923 1,626,573 Davis Apr. 26, 1927 1,689,506Toyoda Oct. 30, 1928 1,749,120 Baker Mar. 4, 1930 1,758,738 Draper May13, 1930 FOREIGN PATENTS Number Country Date 8,225 Great Britain Oct.17, 1905 33,199 Sweden Oct. 20, 1910 103,201 Switzerland Jan. 16, 1924274,473 Great Britain Dec. 1, 1927 876,944 France Aug. 24, 1942

